Stress fracture

This article is about stress fractures in bones. For stress fractures in engineering, see fractureand fatigue (material).

A stress fracture is a very small sliver or crack in the bonethat is accompanied by intense pain.

There are many types of stress fractures. One of the most commonly known is a tibiastress fracture. The tibia is a weight-bearing bone; therefore, when a stress fracture occurs on it, it takes much longer to heal than one on a non-weight-bearing bone. Another common type occurs in the metatarsalsof the feet. These also take quite a while to heal because the feet are constantly facing weight. A third type of stress fracture is known as the fibulastress fracture. The fibula is non-weight-bearing bone; therefore, when a stress fracture occurs on it, it takes less time to heal than one on a weight-bearing bone.

Causes

Bones are constantly attempting to remodel and repair themselves, especially during a sport where excessive stress is applied to the bone. Over time, if enough stress is placed on the bone that it is higher than that of the remodeling, a weakened site -- a stress fracture -- on the bone may appear.

Musclefatigue can also play a role in the occurrence of stress fractures. For every mile a runner runs, more than 110 tons of energy must be absorbed by the legs. Bones are not made to stand that much energy on their own and the muscles act as shock absorbersfor the excess force. But, as muscles become tired and stop absorbing most of the shock, the bones experience greater amounts of stress. Finally, when muscles (usually in the lower leg) become so fatigued that they stop absorbing any shock, all forces are transferred to the bones.

Frequency

Dr. Johnathan C Reeser states that, in the US, the annual incidence of stress fractures range from 5% to 30%, depending on the sport and other risk factors. Stress fractures occur less frequently in African Americanscompared to whitesdue to a higher BMD(bone mineral density). Womenand highly-active individuals are also at a higher risk. The incidence probably also increases with age due to age-related reductions in BMD. But childrenmay also be at risk because their bones have yet to reach full density and strength.

Symptoms

Stress fractures usually have a narrow list of symptoms. It includes a generalized area of pain, increased pain when pressure is applied, and pain with weight-bearing. Usually when running, a stress fracture has severe pain in the beginning of the run, moderate pain in the middle of the run, and severe pain at the end and after the run.

Workup

X-raysusually do not show any evidence of stress fractures, so a CT scan, MRI, or 3-phase bone scanmay be more effective in diagnosing a stress fracture.

Treatment

Rest is the only way to completely heal a stress fracture. The average time of complete rest from the activity that caused the stress fractures is four to twelve weeks. During this time, it is advised that training errors be identified (for instance, too much, too soon) and avoided in the future. One rule of thumb is to not increase the volume of training by more than 10% from one week to the next.

Rehabilitationusually consists of muscle strength training to help dissipate the exessive forces transmitted to the bones.

In some cases, an electronic stimulator or bone stimulator may be used. These devices send electrical impulses into the bone to promote healing; recent studies have shown that the bone heals naturally via electromagneticstimulation. Electromagnetically stimulating the bone causes the bone to lay out more bone cells that strengthen the bone.

Bracing or casting the limb with a hard plastic boot or air castmay also prove beneficial by taking some stress off the stress fracture. An air cast has pre-inflated cells that put light pressure on the bone, which promotes healing by increasing blood flow to the area and takes away a lot of the pain because of the pressure it applies to the bone. If the stress fracture is severe enough, crutches also help to take all stress off the bone.

With severe stress fractures, surgerymay be needed for proper healing. The procedure may involve pinningthe fracture site, and rehabilitation takes an average of six months.

Prevention

One method of avoiding stress fractures is by adding more stress to the bones. Although counter-intuitive given that stress fractures are caused by too much stress on the bones, when moderate stress is applied to the bone in a controlled manner, the bone becomes stronger and less susceptible to a stress fracture. An easy way to do this is to follow one widely known rule for runners, which states that mileage should be increased by no more than 10% per week. This allows the bones to adapt to the added stress so they are able to withstand greater amounts of stress in the future.

Strengthening exercises also help build more muscle strength in the legs. Strengthening these muscles will stop them from getting fatigued so quickly, which allows them to absorb the pounding of running for longer periods of time. Key muscles that need to be strengthened with lower leg stress fractures are the calvesand the shinmuscles.

Depending on a variety of factors including weight, running surface and shoe durability, runners should replace their shoesevery 300-700 miles to allow adequate mid-sole cushioning. A change in the choice of running surfaces can also help prevent stress fractures.

When performing any exercise that applies more stress to the bones, it may be wise to up calciumand vitamin Dintake, depending on the individual. Also, it is important to monitor foods eaten because nutritionplays a vital role in bone development.

References

• Reeser, Johnathan C., MD, PhD. (2004, October 1). Stress Fracture. eMedicine. Retrieved April 29, 2005 from the World Wide Web: http://www.emedicine.com/pmr/topic134.htm

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It uses material from the http://en.wikipedia.org/wiki/Stress+fracture Wikipedia article Stress fracture.